This invention relates to a method of heating by means of a specific mixture of fluids employed as the working agent in a heat pump. U.S. Pat. No. 4,089,186, discloses the use of mixtures in heat-pumps, so as to improve the performance thereof by vaporizing and condensing the mixture in accordance with temperature profiles parallel to those of the external fluids with which the heat exchanges are performed, these heat exchanges being of the counter-current type.
The mixtures are defined in the U.S. Pat. No. 4,089,186, as comprising at least two constituents whose composition does not result in an azeotropic mixture.
The embodiments disclosed in the U.S. Pat. No. 4,089,186, relate to cases where heat is recovered in a wide temperature range. This explains why the U.S. Pat. No. 4,089,186, discloses a preferred embodiment according to which the mixture circulated in the heat-pump is condensed in two stages, so as to supply heat in a narrower temperature range than the temperature range at which heat is recovered. However, in the above embodiment the mixture condenses in a temperature range which comprises temperatures in excess of 40.degree. C.
When heat is recovered in a wide temperature range and the mixture is a binary mixture, the proportions of the two constituents forming the mixture must not be too different. Thus, in the two examples of the U.S. Pat. No. 4,089,186, the mixture consists of 40% chloro-difluoromethane (R-22) and 60% 1,1,2-trichloro-1,2,2-trifluoro ethane (R-113) in one case and 38% propane and 62% normal pentane in the other case.
In another type prior art, the heat-pumps used for heating buildings require other working conditions. As a matter of fact, in many cases, heat is recovered in a relatively narrow temperature range of, for example, 5.degree. to 15.degree. C. These heat-pumps often operate by recovering heat from a fluid, such as water or air, whose temperature is relatively low, for example between 0.degree. and 20.degree. C., and delivering heat to a fluid, such as water or air, whose temperature is also relatively low, for example, between 20.degree. and 40.degree. C.
When using such heat-pumps, the conventionally used working fluid is either monochlorodifluoromethane (R-22) or dichlorodifluoromethane (R-12); the critical temperature, which will be hereinafter called t.sub.c, is 96.degree. C. for R-22 and 112.degree. C. for R-12.
As a rule, the higher the boiling temperature and the critical temperature, the more favorable the performance rate; this leads, however, to a high suction rate, thus to a reduced heat capacity for any given compressor employed in the system. The selection of R-22 and R-12 results from a compromise between these two requirements, and as concerns the conventional temperatures used in house-heating, the use of R-12 being more appropriate to relatively high temperature levels, for example, higher than 50.degree. C.
It is usually preferred that these heat pumps be operated with halogenated fluids of the "Freon" type for safety reasons, thus avoiding inflammable materials such as hydrocarbons or toxic materials such as ammonia.